1. Field of the Invention
The present invention relates to a fixing unit configured to fix a toner image on a sheet, and to an image forming apparatus with the fixing unit.
2. Description of the Related Art
Heating by electromagnetic induction is more rapid and efficient heating manner. Therefore, heating by electromagnetic induction (hereinafter called “induction-heating” or “IH”) is used for various apparatuses. For example, a particular image forming apparatus comprises an induction-heating type of a fixing apparatus.
A distance between a magnetic body through which a magnetic flux passes and an object to be induction-heated in an induction-heating type of an apparatus is a very important parameter. For example, in the case of the induction-heating type of the fixing apparatus, variation in the distance between the magnetic body and the object to be induction-heated results in irregular temperature over the object, which in turn leads to degrading a toner image fixed on a sheet. A particular fixing apparatus comprises a magnetic tube configured to cover a shaft. The magnetic tube is coaxially disposed inside a roller configured to fix an image to keep a consistent distance between the magnetic tube and the roller. The shaft is typically made of metal to reduce twisting of the shaft.
A current flows in a coil during induction-heating. The shaft of the fixing apparatus described above is separated by a sufficient distance from the coil. Consequently, the current is less likely to leak into the shaft. However, if a fixing apparatus including a metal shaft comprises a magnet body closer to a coil, it is required to electrically insulate the coil from the metal shaft.